This tables gives the expected R_V values appropriate to use for broad-band photometry as a function of model and E(B-V)_CCM89. I have used the Bessel (1990) B and V filter functions, and adopted a CCM89 reddening law with R_V=3.1. For each model I show the effective wavelengths of the B and V filers (first two columns) with zero reddening. For an E(B-V)_CCM89=1.0, 2.0, and 3.0 I show the derived A_V and expected E(B-V) [broad-band]; the ratio is by definition the effective R_V to use. Thus, for instance, for a small amount of reddening [first row] the value of A_V is 3.076, and the corresponding color excess is 0.774. The ratio is 3.98. Thus if you had a 3400 K star with a surface gravity of 0.5 and an A_V of about 3, a good value of R_V to use would be 4.0. Surface gravity has a larger effect on the B-filter than on the V-filter (as one might expect) and so there is actually a significance difference in the effective R_V with log g: the differences are typically about 0.3 in R_V! The effect with the amount of reddening is comparable, about 0.2. On average, a value of 4.3 is reasonable for log g=0.0 and a "modest" amount of reddening. These have all been computed using the Galactic metallicities.... E(B-V)_CCM89=0.0 E(B-V)_CCM89=1.0 E(B-V)_CCM89=2.0 E(B-V_CCM89)=3.0 ---------- ---------------------------- ----------------------------- ---------------------------- Model B V B V Av E(B-V) R_V B V Av E(B-V) R_V B V Av E(B-V) R_V 3400g0.5 4587. 5527. 4708. 5611. 3.076 0.774 3.98 4823. 5703. 6.100 1.480 4.12 4923. 5801. 9.067 2.136 4.24 3400g0.0 4623. 5534. 4738. 5617. 3.072 0.743 4.13 4846. 5709. 6.091 1.427 4.27 4939. 5806. 9.055 2.066 4.38 3400g-0.5 4656. 5543. 4766. 5626. 3.066 0.717 4.27 4867. 5717. 6.080 1.381 4.40 4955. 5813. 9.039 2.007 4.50 3500g0.5 4626. 5552. 4735. 5633. 3.061 0.754 4.06 4838. 5720. 6.071 1.451 4.18 4930. 5811. 9.029 2.104 4.29 3500g0.0 4656. 5562. 4760. 5643. 3.054 0.731 4.18 4857. 5729. 6.059 1.412 4.29 4943. 5819. 9.011 2.054 4.39 3500g-0.5 4684. 5573. 4784. 5654. 3.047 0.711 4.28 4876. 5739. 6.045 1.377 4.39 4958. 5829. 8.991 2.009 4.48 3600g0.5 4646. 5572. 4749. 5651. 3.048 0.748 4.08 4845. 5735. 6.047 1.445 4.19 4931. 5821. 8.997 2.102 4.28 3600g0.0 4673. 5581. 4771. 5660. 3.043 0.728 4.18 4862. 5743. 6.037 1.411 4.28 4944. 5829. 8.981 2.058 4.36 3600g-0.5 4698. 5590. 4792. 5669. 3.037 0.709 4.28 4879. 5752. 6.025 1.378 4.37 4957. 5837. 8.965 2.015 4.45 3700g0.5 4656. 5583. 4755. 5661. 3.042 0.746 4.08 4847. 5743. 6.035 1.443 4.18 4930. 5827. 8.980 2.104 4.27 3700g0.0 4680. 5589. 4775. 5667. 3.038 0.726 4.18 4863. 5749. 6.028 1.410 4.28 4942. 5832. 8.969 2.059 4.35 3700g-0.5 4704. 5595. 4795. 5674. 3.034 0.708 4.29 4879. 5756. 6.019 1.376 4.37 4955. 5839. 8.957 2.016 4.44 3800g0.5 4659. 5585. 4757. 5663. 3.041 0.744 4.09 4847. 5744. 6.033 1.441 4.19 4929. 5827. 8.977 2.103 4.27 3800g0.0 4682. 5588. 4775. 5667. 3.038 0.725 4.19 4862. 5748. 6.028 1.407 4.28 4940. 5831. 8.970 2.058 4.36 3800g-0.5 4704. 5593. 4795. 5672. 3.035 0.706 4.30 4878. 5754. 6.022 1.374 4.38 4953. 5836. 8.960 2.014 4.45 3900g0.5 4658. 5581. 4755. 5660. 3.043 0.743 4.10 4845. 5741. 6.037 1.439 4.19 4927. 5823. 8.983 2.100 4.28 3900g0.0 4679. 5583. 4773. 5662. 3.041 0.724 4.20 4860. 5744. 6.034 1.406 4.29 4938. 5826. 8.979 2.056 4.37 3900g-0.5 4701. 5588. 4791. 5667. 3.039 0.706 4.30 4875. 5748. 6.029 1.374 4.39 4950. 5831. 8.970 2.013 4.46 4000g0.5 4654. 5574. 4752. 5653. 3.047 0.743 4.10 4843. 5735. 6.045 1.439 4.20 4924. 5818. 8.995 2.098 4.29 4000g0.0 4673. 5576. 4769. 5656. 3.046 0.725 4.20 4856. 5737. 6.043 1.407 4.29 4935. 5820. 8.991 2.056 4.37 4000g-0.5 4694. 5581. 4786. 5661. 3.043 0.709 4.29 4871. 5742. 6.037 1.377 4.38 4947. 5825. 8.982 2.016 4.45 4100g0.5 4647. 5567. 4747. 5646. 3.052 0.744 4.10 4839. 5728. 6.054 1.441 4.20 4921. 5811. 9.008 2.100 4.29 4100g0.0 4665. 5569. 4762. 5649. 3.050 0.728 4.19 4852. 5731. 6.051 1.412 4.29 4931. 5814. 9.003 2.061 4.37 4100g-0.5 4684. 5574. 4779. 5654. 3.047 0.713 4.27 4865. 5736. 6.045 1.385 4.36 4942. 5819. 8.993 2.025 4.44 4200g0.5 4638. 5560. 4740. 5639. 3.056 0.748 4.08 4834. 5721. 6.063 1.446 4.19 4918. 5805. 9.020 2.106 4.28 4200g0.0 4655. 5563. 4754. 5643. 3.054 0.734 4.16 4846. 5725. 6.059 1.421 4.26 4927. 5808. 9.014 2.072 4.35 4200g-0.5 4673. 5569. 4770. 5648. 3.051 0.720 4.24 4859. 5730. 6.052 1.396 4.34 4937. 5814. 9.004 2.039 4.42